Topic: Drilling discs

[timtune]

I want to drill my discs and I'm wondering how hard they are to drill. Any special type of drill required?

[Shtonecb500]

the better the drill press you have, the better your results, what really matters are the drill bits and oil lubrication. There are hole templates online you can print, lay over your rotor and mark out the holes, or you can find a shop who will do it all by computer.

Its just time consuming.

[Don R]

  The above and center punch the starting point, I use a small bit to establish a center so the bit doesn't wander. Watch for the long shaving coming off they are sharp and get a good cutting oil to lube the drill with. 

[Alan F.]

I remember running a fan as hot cutting oil gets smoky, and you'll be at it a while.

[MauiK3]

Maybe have more than one drill bit, the material really dulls them quickly.
Mine were done at True Disk
https://truedisk.net

Great work

[willbird]

I did mine in a Bridgeport mill. Just used a good quality High Speed Steel drill bit.

[Bodi]

They are not very hard as in Rockwell hard. But stainless steel is weird to machine. It can grab and/or dull tools Don't go tiny steps in drill sizes - that is begging to grab and snap a drill bit. Centre drill and then go maybe 2 steps if you want fairly big holes.
Invest in a few center drills and start each hole with one. These are short and stubby so they don't wander on starting - but still centre punch each hole to have an accurate position.
Cutting speed is critical. I don't know what type of SS they are, so looking up the "ideal" cutting speed is not so possible.
You want to use slow enough RPM that the drill's cutting edge cuts through under the work hardened layer from the last cut: fast RPM would mean pushing through at a ridiculous feed rate to do that. Choke the drill in the chuck with minimum sticking out to reduce torsional vibration.
Use cutting fluid for sure. If you can drill through into a mild steel plate clamped under the disc, you get a super clean hole exit.
You should see nice clean long chips. If they are small broken chips you're not feeding fast enough or something is wrong with the drill grind or rpm.
There's some debate on chamfering. If the idea is to clean water off for wet braking, I've read that chamfering reduces that effect.
If you have a good drill (with the right grind but that's another story, SS wants a certain cutting angle with no undercut on the edge), run the right speed, drill into a steel backing, and use some cutting oil, the holes don't need chamfering. I did one with chamfering and one with clean holes that I went over with an India stone to remove any high spots. Those holes look really nice (way better than chamfered). I think the wet performance is better (probably imagination) and there is no cheese grater type wear on the pads as is sometimes given as a reason for the chamfers. I looked at some factory drilled and slotted discs and they didn't have chamfers.

[Tracksnblades1]

I second all the suggestions.

If you’re using a drill press, after good center punch transfer of your pattern, I like using a lathe center drill bit. See picture. It has very little deflection and is primarily used to start the hole on the center punch. I don’t clamp the piece down until the center drill bit finds its center on the center punch mark. Then with light pressure down on the center drill (drill press off) clamp down your piece tight change drill bit and drill. While still clamped change to chamfer bit and chamfer. Works good by hand too, but is not as accurate.  Center punch, center drill, drill, chamfer, repeat, repeat, repeat. 😇

And the local machine shop here says real cow’s butter or real lard makes for a good stainless steel drill bit coolant. Never tried either. But I know “DevTap” (trichloroethylene) used to be the best  on 300 series stainless, but like so many things it’ll cause you to have blind pups if it soaks into your skin or breathe the fumes..😜



For really accurate hole a Bridgeport with a dividing head mounted on the table. It’ll test your math with your pattern you chose. 😁

[lash]

Would these make your life easier?

[Bankerdanny]

I sent mine to Jeff at Godferry's Garage in Wisconsin. In addition to drilling he thins them and replaces the hardware that attaches the rotor to the hub. If you want to add a 2nd disk to your front he will countersink the bolt holes to make it easier.

I highly recommend him. https://godfferysgarage.com/

[opp750]

I have a drilled disc from 4into1 installed on my in-progress build of a 75 cb550. It is defiantly not chamfered. Was I supposed to chamfer before I installed it – or are they fine as is? Kinda seems like something they should have mentioned if the answer is yes.

[grcamna2]

subscribed

[timtune]

I sent mine to Jeff at Godferry's Garage in Wisconsin. In addition to drilling he thins them and replaces the hardware that attaches the rotor to the hub. If you want to add a 2nd disk to your front he will countersink the bolt holes to make it easier.

I highly recommend him. https://godfferysgarage.com/

Those bring up my next question. How much material can I remove? Those look like they would be close to the limit.

[Shtonecb500]

people have brought up goddfrey discs maybe being too thin to handle heavy braking duties anymore but people chimed in and confirmed there are no issues with his rotors.

[timtune]

Would these make your life easier?

Is the last pic showing it bead blasted? Looks like it would be "sanding" the pads.

[MauiK3]

Honda wanted to make sure the discs were beefy enough to handle heat. Being the first of its kind, the CB 750 could not afford to be seen as deficient in this capacity. Modern brakes are much better but back then no one had seen such a thing as a hydraulic disc brake on a large motorcycle.

[Shtonecb500]

i would just buy a set off the guy who posted above lol.

[lash]

These were blasted to clean them up and haven’t been turned yet. I could have them turned fairly easily. Just haven’t done that because I was never planning on using them.
Shoot me an email.

[Godffery]

I sent mine to Jeff at Godferry's Garage in Wisconsin. In addition to drilling he thins them and replaces the hardware that attaches the rotor to the hub. If you want to add a 2nd disk to your front he will countersink the bolt holes to make it easier.

I highly recommend him. https://godfferysgarage.com/

Those bring up my next question. How much material can I remove? Those look like they would be close to the limit.

I am not disparaging Godferry’s work, but there is a practical limit to material mass to dissipate heat generated through braking, as well as stress on thin material (especially stainless). If you punch too many holes and thin the discs too far, they will not endure and are more prone to warp age from heat.

Modern rotors have hole and slot patterns that are a mathematical ratio to the mass and surface area. Do the calculations and be your own judge on how much is enough or too much.

Figured I'd chime in here.
While developing my Drilled & Thinned Rotors, I tested a number of hole size and quantities, hole Placement and overall rotor thickness (with many of them being tortured on the AHRMA circuit) to get the right combination.
 As for chamfering the drill holes; Resurfacing is the best solution for dealing with the distortion around the holes caused by drilling.  Putting a chamfer on them will not necessarily remove all the distortion, depending how well the drilling is done. So some holes will require deeper chamfers to remove the distortion, but this causes another issue. The chamfer will act as a ramp and allow debris to be embedded into the brake pads, causing damage to both the pads and the rotor, as well as loosing braking efficiency and add to unnecessary heating.

[ekpent]

Pop quiz - Which year and model of motorcycle was the first to come with factory dual front rotors/brakes ?

[Tracksnblades1]

Pop quiz - Which year and model of motorcycle was the first to come with factory dual front rotors/brakes ?

1973 BMW R90S

😁

[seanbarney41]

Pop quiz - Which year and model of motorcycle was the first to come with factory dual front rotors/brakes ?

Suzuki water buffalo...not sure what year...'74?

[seanbarney41]

I have had Goddfrey drilled and thinned rotors on my 750f for over 12,000 miles now.  Lot's of hard braking,  It still stops great.  No warping.  Also did gl1000 discs on my gold 750k...same deal, really good work making old parts work wayyy better than they did new even after thousands of miles of hard use.

[ekpent]

Pop quiz - Which year and model of motorcycle was the first to come with factory dual front rotors/brakes ?

Suzuki water buffalo...not sure what year...'74?

I've read where the 1973 Suzuki GT750 was the first so I,m giving the chicken dinner to Sean if I can maybe have a leg. I'll have to check out the Beemer to see what's up, maybe what I read meant first JAP bike ??

[Godffery]

I have had Goddfrey drilled and thinned rotors on my 750f for over 12,000 miles now.  Lot's of hard braking,  It still stops great.  No warping.  Also did gl1000 discs on my gold 750k...same deal, really good work making old parts work wayyy better than they did new even after thousands of miles of hard use.

Thanks for the good word Man!